Most bacteria use sugars and vegetable oils, which are biomass, as source, and accumulate polyhydroxyalkanoates (PHAs) as energy storage materials in cells (Non Patent Literatures 1 to 3). Since PHAs have biodegradable and thermoplastic properties, they are expected to be applied as an alternative to petroleum-based plastic (Non Patent Literatures 4 and 5).
In addition, since PHAs have biodegradable and biocompatible properties, they are also expected to be applied as biomaterial (Non Patent Literatures 6 and 7). It has been reported that PHAs have high affinities with bone and cartilage tissues (Non Patent Literature 8), blood (Non Patent Literature 9), and various cell lines through in vivo and in vitro experiments, and PHAs are expected to be used in the medical field.
Intracellular synthesis of a PHA in a microbial cell is carried out by supplying a hydroxyacyl-CoA as a monomer from the metabolic pathway using carbon source as source and polymerizing the supplied monomer by a PHA synthase. As such, the intracellular synthesis of the PHA is characterized in that all of the reactions including supplying a monomer and synthesizing a polymer are carried out in the microbial cell. In the present system, a kind or composition of the monomer constituting the PHA is determined by a kind of the carbon source to be supplied, the metabolic pathway, and substrate specificity of the PHA synthase. In order to adjust these factors, culture conditions and carbon sources have been adjusted, and new metabolic pathways have been established by combining genetic engineering methods and metabolic engineering methods, and thus, more than 100 kinds of PHA families have been reported so far (Non Patent Literature 10). Most of the reported PHA families are PHAs having a variety of side chains. As PHAs having a variety of main chains, only a few PHAs such as lactate (Non Patent Literature 11), 4-hydroxybutyrate (4HB) (Non Patent Literature 12), 4-hydroxyvalerate (4HV) (Non Patent Literature 13), 5-hydroxyvalerate (5HV) (Non Patent Literature 14), and 6-hydroxyhexanoate (6HH) have been reported.